Oil burner spark ignition system

ABSTRACT

AN OIL BURNER IGNITION SYSTEM PRODUCES A TONGUE-LIKE CONFIGURATION OF INDIVIDUAL SPARKS EXTENDING FROM A PAIR OF DISCHARGE ELECTRODES AND INTO THE SPRAY PATTERN OF OIL PARTICLES PRODUCED BY THE BURNER NOZZLE. THE SYSTEM INCLUDES A SPARK GENERATING RELAXATION OSCILLATOR CIRCUIT CAPABLE OF PRODUCING INDIVIDUAL SPARKS AT A FREQUENCY SUCH THAT SUBSEQUENT SPARKS ARE ABLE TO FOLLOW THE ELONGATING IONIZED AIR PATH ESTABLISHED BY PREVIOUS SPARKS. THE OSCILLATOR CIRCUIT INCLUDES A CAPACITOR CHARGED FROM AN AC POWER SOURCE AND REPTITIVELY DISCHARGED DURING ALTERNATE HALF CYCLES AT RAPID INTERVALS THROUGH THE PRIMARY WINDING OF A TRANSFORMER BY MEANS OF A CONTROLLED RECTIFIER GATED IN ACCORDANCE WITH THE CAPACITOR CHARGE LEVEL.

Jan. 19, 1971 v R. H. CAMPBELL 3,556,706

I OIL BURNER SPARK IGNITION SYSTEM Filed July 16, 1 969 66 5 I v 2 I 5s44 z g INVEN'TORI RICHARD H. CAMPBELL BY: mason KolelqmovinQ-n PatentedJan. 19, 1971 US. Cl. 431265 3 Claims ABSTRACT OF THE DISCLOSURE An oilburner ignition system produces a tongue-like configuration ofindividual sparks extending from a pair of discharge electrodes and intothe spray pattern of oil particles produced by the burner nozzle. Thesystem includes a spark generating relaxation oscillator circuit capableof producing individual sparks at a frequency such that subsequentsparks are able to follow the elongating ionized air path established byprevious sparks. The oscillator circuit includes a capacitor chargedfrom an AC power source and repetitively discharged during alternatehalf cycles at rapid intervalsthrough the primary winding of atransformer by means of a controlled rectifier gated in accordance withthe capacitor charge level.

The present invention relates to ignition systems for fuel oil burners.

A conventional fuel oil burner includes a nozzle for creating a spraypattern of oil particles in an air stream produced by a blower. In orderto ignite the oil particles emerging from the burner nozzle, thetraditional method is to mount a pair of spark electrodes upstream inthe air stream from the spray pattern and to provide a substantiallycontinuous stream of sparks with a large and expensive transformercoupled to an AC supply. Sparks produced in this manner are capable offorming a tonguelike spark extension in the air stream projecting fromthe electrodes into the spray pattern.

Due to the size, weight, expense and power consumption of conventionalspark transformers, it has been proposed to provide solid state ignitionof fuel oil burners. Some devices of this type introduced to date havenot produced sparks capable of forming into a tongue-like extension, andas a result have required location of the spark electrode tips withinthe oil spray pattern. This approach is subject to several disadvantagesincluding the fact that when the electrodes are located in the oil path,carbon forms on the electrodes eventually bridging the spark gap andresulting in unreliable ignition. In addition, impinging oil deflectedfrom the spray pattern may reach the combustion area in an unatomizedform, resulting in an undesirable smoky fire. Furthermore, interferenceby the electrodes with the spray pattern can disturb the uniformity ofthe pattern to such an extent that unstable, lopsided and noisycombustion takes place.

In order to overcome such disadvantages, it has been proposed to producewith asolid state ignition device a low frequency series of individualsparks each having a size and duration capable of being diverted by theair stream into the spray pattern. Devices of this character developedheretofore, however, have been subject to the disadvantages of highpower consumption, expense and questionable reliability in operation.

Among the important objects of the present invention are to provide animproved oil burner ignition system characterized by small size, lowcost, and reliability; and to provide an improved solid state fuel oilignition system capable of producing a tongue-like extension of sparksin an air stream.

In brief, an oil burner ignition system constructed in accordance withthe present invention serves to ignite an oil burner of the typeproducing a spray pattern of oil particles in an air stream. Theignition system includes a pair of spark discharge electrodes havingspaced tip portions forming a spark gap and being located upstream inthe air stream from the spray pattern and out of the path of the oilparticles. In accordance with an important feature of the invention, arelaxation oscillator generates at the spark gap a series of individualsparks at a frequency such that a series of sparks traverse an ionizedair path or region and are deflected from the spark gap into the spraypattern for ignition of the oil particles. A first circuit loop of theoscillator circuit includes a pair of power supply terminals adapted tobe connected to an AC power source for charging a capacitor in apredetermined polarity during alternate half cycles of the power supplyvoltage waveform. A second circuit loop includes the primary winding ofa transformer and the capacitor, together with the output terminals of acontrolled rectifier. A trigger circuit for the rectifier places therectifier in a conductive condition in response to a predeterminedcapacitor charge level, and the capacitor discharges in a current pulsethrough the primary winding thereby to produce a spark at the sparkelectrodes coupled to the secondary winding of the transformer. Thecontrolled rectifier is returned to a nonconductive condition inresponse to production of the current pulse whereupon the capacitorrecharges and subsequent sparks are produced. Since the system producesa train of individual short duration high frequency sparks rather thanlow frequency long duration sparks, the circuit design is simplified andthe power consumption is significantly reduced.

The invention together with the above and other objects may be betterunderstood from consideration of an illustrative embodiment shown in theaccompanying drawing.

The single figure of the drawing includes a somewhat diagrammaticsectional view of a fuel oil burner together with a diagrammatic andschematic illustration of an ignition system for the burner.

Referring now more specifically to the drawing, there is illustratedpart of an oil burner 10 equipped with an improved ignition systemdesignated as a whole by the reference numeral 12 and constructed inaccordance with the principles of the present invention. In accordancewith important features of the present invention, the ignition system 12is compact in size, light in weight, does not require a substantialamount of power for operation, and in operation serves to produce aseries of individual high frequency sparks capable of establishing adeflectable ionized air path to the end that the ignition system 12 doesnot intrude upon or interfere with the oil particles emitted by theburner 10.

The burner 10 may be of conventional construction and includes a drafttube 14 Within which is centrally disposed a nozzle 16 supplied withpressurized fuel oil from a suitable pump or the like by means-"0f anoil conduit 18. Air is supplied to the draft tube 14 by a suitable fanor blower (not shown) and moves in a stream through a wall structure 20defining an array of swirl vanes 22. The air stream emerges from theburner 10 through an aperture 24 in a choke plate 26, and the swirlvanes 22 and choke plate 26 combine to impart a turbulent swirlingmotion to the air stream.

Oil expelled from the nozzle 16 is atomized and forms a spray pattern ofoil particles designated by the numeral 28. In the illustratedarrangement the spray pattern is substantially conical in shape.Interaction between the swirling turbulent air stream and the emergingoil particles in the region of the choke plate 26 causes some divergenceof oil particles from the true conical array of particles,

and the actual interface between the spray pattern and the air stream isnot well defined and may vary by as much as one-eighth inch or so,

In order to ignite the oil particles in the spray pattern 28, theignition system 12 includes a pair of spark discharge electrodes 30 and32 supported by a pair of insulators 34 and 36 carried by the wallstructure 20. A pair of angularly offset electrode tip portions 30A and32A define a spark gap 38 which may have a length in the neighborhood ofone-eighth to three-sixteenth inch. Advantageously, the spark gap 38defined between the tip portions 30A and 32A is spaced sutficiently fromthe spray pattern 28 so that the electrodes are not contacted by oilparticles expelled from the nozzle 16. For example, the electrode tips30A and 32A may be located onequarter inch upstream in the moving airstream from the normal boundary of the spray pattern 28 so thatdisturbances in the spray pattern caused by the turbulent air stream donot result in oil particles striking the elec trodes. As a result, theproblem of carbon formation on the electrodes is greatly diminished, andsince the electrodes do not interfere with the spray pattern, a cleanburning, even and quiet combustion condition is maintained.

One important aspect of the present invention resides in the ability ofthe ignition system 12 to produce a high frequency series of individualsparks at the spark gap 38 in order that a tongue-like extension ofsparks is deflected by the moving air stream from the gap 38 and intothe spray pattern 28 for the ignition of the oil particles. The system12 includes a relaxation oscillator circuit generally designated as 40coupled by means of a transformer 42 to the electrodes 30 and 32 forproducing the highly desirable high frequency spark action at theelectrodes.

More specifically, the oscillator circuit 40 includes a pair of powersupply terminals 44 and 46 adapted to be connected to a standard sixtycycle AC power supply having a rated line voltage in the neighborhood of120 volts. During alternate half cycles of the voltage waveform when theterminal 44 is positive with respect to the terminal 46, the oscillatorcircuit 40 is effective to produce a series of individual sparks at ahigh frequency. When the terminal 44 becomes positive relative to theterminal 46, a capacitor 48 is charged by a current flowing in a firstcircuit loop through a current limiting resistor 50 and an inductor orchoke 51. The capacitor 48 is permitted to become charged due to theinitially nonconductive condition of a controlled rectifier 52.

In order to control discharge of the capacitor 48, there is provided atrigger circuit 54 coupled between the capacitor and the gate electrodeof the controlled rectifier 52 for rendering the controlled rectifier '2conductive when a predetermined capacitor charge level is attained. Thetrigger circuit includes a resistor 58 and a variable resistor 60, thesetting of which determines the firing point of the controlled rectifier52. A resistor 56 provides stabilizing gate bias on the controlledrectifier for preventing spurious triggering due to internally generatedleakage currents. A capacitor 62 provides a slight delay phase shift,and a diode 64 is included to prevent an excessive and possibly damagingvoltage drop between the cathode and gate electrodes of the controlledrectifier 52.

When the controlled rectifier 52 is rendered conductive, the capacitor48 rapidly discharges in a current pulse through a second circuit loopincluding the capacitor 48, a current limiting resistor 66, theanode-cathode circuit of the controlled rectifier 52 and a primarywinding 68 of the transformer 42. A secondary winding 70 of thetransformer 42 is connected to the electrodes 30 and 32 and includessubstantially more turns than the primary 68 to provide a high voltagefor generation of an arc at the spark gap 38. The transfer of energyinto the spark gap may be substantially improved by choosing theelectrical values of the circuit so that resonance takes place at afrequency approximating that of the generated pulse.

Upon discharge of the capacitor to produce a spark, the controlledrectifier 52 is returned to its nonconductive condition in preparationfor another cycle of operation. More specifically, when the controlledrectifier 52 becomes conductive, the inductance 51 acts as a choke toprevent rapidly increasing current flow from the power supply terminals44 and 46. The collapsing field associated with the primary winding 68of the transformer 42 imposes a reverse voltage through the capacitor 48across the anode and cathode of the controlled rectifier 52, thereby toreturn it to its nonconductive condition. Preferably the rectifier issubjected to a substantial reverse bias to provide positive turnoff andto increase the frequency of operation. As a result, the capacitor 48again is permitted to become charged until the trigger circuit 54 againrenders the controlled rectifier 52 conductive to produce another spark.

The sparking operation continues repetitively throughout the half cycleof the power supply waveform until the power supply voltage is incapableof charging the capacitor to the extent necessary for operation of thetrigger circuit 54. The oscillator then remains inactive during thefollow-ing half cycle of reverse polarity and operates once more in thesecond following half cycle. Since the oscillator is energized directlyby an AC supply, rather than by DC, the reverse polarity excursions ofthe power supply render the controlled rectifier 52 nonconductive in theevent that the negative voltage pulse normally turning off the rectifieris interrupted or the like. Thus, the reliability of the circuit isimproved because the oscillator is effectively returned to its initialcondition prior to each positive excursion of the power supply voltagewaveform.

It is critical in carrying out the present invention that the frequencyof operation of the relaxation oscillator circuit 40 be sufficient sothat a tongue-like extension of spark is created in the air stream atthe spark gap 38. Having reference to the mechanism of the arc inthe airstream at the gap 38, when an arc is struck by an initial high voltagejump across the shortest path between the two spaced electrode tips 30Aand 32A, the air path traversed by the arc is ionized and consequentlyexhibits an abrupt drop in impedance. The arc continues over the ionizedpath, and due to the movement of air through the region of the spark gapthe ionized path is displaced downstream and becomes elongated. At somepoint the combination of decreasing voltage at the spark gap andincreasing length of the low impedance ionized air path causes the arcto become extinguished. For a period of time after the arc isextinguished, the ionized region persists adjacent the electrodes. Ifthe subsequent spark is produced soon enough, the arc is reestablishedin the region of ionized air remaining from the previous spark. Sincethe region of ionized air is continually moved downstream, the arc canbe extended into the spray pattern 28 to ignite the oil particles ,eventhough the electrode tips 30A and 32A are located as much as one-quarterinch or more from the spray pattern region.

The frequency of operation is important to carrying out this result. Forexample, many known solid state ignition devices produce sparks at therate of one spark during each half cycle of the power supply ACwaveform. With such an extended duration of time between sparks, it isimpossible for subsequent sparks to produce arcing across the ionizedair path established by previous sparks, and the tongue-like sparkextension of several individual sparks cannot be achieved.

In conventional oil burner apparatus the velocity of the moving airstream may range from as high as fifty feet per second to a much smallervalue. In order to produce the desirable result of the presentinvention, it is necessary for the frequency of spark production to beno less than about several thousand sparks per second. As a practicalmatter, it is believed that under ordinary conditions about twenty-fivehundred sparks per second is the minimum rate which will produce thedesired spark tongue extension, while a considerably higher frequency isdesirable in order to produce sparks having a desirable hot, fatappearance.

Another advantage of the high frequency of operation of the relaxationoscillator circuit 40 is that the cost of the transformer 42 is reduced.More specifically, at a high operating frequency the impedance of thetransformer is such that smaller wire and fewer turns can be used thanwould be required at a lower frequency.

In an oil burner ignition apparatus constructed in accordance with thepresent invention, the following specific values, dimensions and detailsof construction produced highly satisfactory results. These specificdetails of the illustrated embodiment are given by way of example only,and other arrangements may be used as well. The spark gap 38 between theelectrode tips 30A and 32A had a length of about one-eighth inch, andthe gap was spaced about one-quarter inch from the normal position ofthe spray pattern 28. The circuit was operated from a standard sixtycycle 120 volt AC power supply, and the controlled rectifier 52comprised a General Electric Company type C-106B1 semiconductorcontrolled rectifier. The transformer 42 included a ferrite core havinga primary winding 68 with 18 turns and a secondary winding 70' with 891turns. The remaining components of the relaxation oscillator circuit hadthe following values:

Resistor 50-70 ohms Resistor 5651O ohms Resistor 5833,000 ohms Variableresistor 60250,000 ohms, maximum Resistor 66 4.0 ohms Capacitor 48-.68microfarad Capacitor 62.O68 microfarad Inductance 52335 millihenries Itwas found that the circuit constructed with these specific componentsperformed in a successful manner and was capable of producing individualsparks at a spark pro duction frequency of about five thousand to abouteight thousand sparks per second during the intervals when theoscillator circuit 40 operated. Consequently, a desirable tongue-likeextension was produced at the spark gap extending well into the regionof the oil particles in the spray pattern 28.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

1. An ignition system for use with a fuel oil burner of the typeproducing a spray pattern of oil particles in an air stream, said systemcomprising:

a pair of spark discharge electrodes having tip portions spaced apart toform a spark gap;

said tip portions being disposed upstream in said air stream from saidspray pattern and out of the path of the oil particles;

an oscillator circuit for producing a series of spark discharges at saidspark discharge electrodes and including a pair of power supplyterminals adapted to be coupled to an AC voltage source;

a transformer having a secondary winding coupled to said electrodes andhaving a primary winding;

a capacitor;

a first circuit loop including said power supply terminals for chargingsaid capacitor in accordance with the voltage source;

a second circuit loop including said primary winding and said capacitor;

a controlled rectifier having a pair of output electrodes and a controlelectrode;

said output electrodes being connected in said second circuit loop forcontrolling the discharge of said capacitor through said second circuitloop;

a trigger circuit coupled between said capacitor and said controlelectrode for rendering said controlled conduction device conductive inresponse to a predetermined capacitor charge level thereby to dischargesaid capacitor in a current pulse through said second circuit loop toproduce an are at said spark discharge electrodes;

and means responsive to production of the current pulse for returningsaid controlled rectifier to the nonconductive condition;

said oscillator being constructed and arranged to pro duce sparks at arate sufiicient to provide a tongue of sparks in said air streamextending into said spray pattern for ignition of said oil particles.

2. The ignition system of claim 1, the rate of spark production beingmore than about twenty-five hundred sparks per second during operationof said oscillator.

3. The ignition system of claim 1, the rate of spark production being inthe approximate range of about five thousand to about eight thousandsparks per second during operation of said oscillator.

References Cited UNITED STATES PATENTS 2,789,632 4/1957 Smits 317-96X2,817,395 12/1957 Lutz et al 431265X 3,142,332 7/1964 Weber et al317-96X 3,207,953 9/1965 Smith et al. 317-96 3,318,358 5/1967 Potts317-96X 3,377,125 4/ 1968 Zielinski 431-74 3,384,440 5/1968 Mayer 431-663,385,527 5/1968 Drewry 431265X 3,457,456 7/1969 Dietz 315-206 VOLODYMYRY. MAYEWSKY, Primary Examiner US. Cl. X.R.

